John T. Richards

Fluorescence lifetime and quenching studies on some interesting diphenylhexatriene membrane probes

Abstract The fluorescence lifetimes of a number of membrane probes based on the 1,6-diphenylhexatriene (DPH) chromophore have been measured in small unilamellar phospholipid vesicles and found to be multiphasic. These probes were quenched by sodium iodide with different efficiencies in vesicles and this has been attributed to the depth of the particular probe in the bilayer. The distribution of the probe between the outer and inner monolayer has been determined for those probes with fixed positions in the bilayer. The iodide ion permeability of the bilayer was found to be immeasurably small over a 3 h period.

Nanosecond laser photolysis of aqueous carbon monoxy- and oxyhaemoglobin

The spectra have been measured of the transient species and the final level of absorption observed in nanosecond laser photolysis of aqueous carbon monoxy- and oxyhaemoglobin. These show that the transient absorption change can be interpreted as being due to an ultrafast ligand recombination following the photolysis. The spectra do not support the earlier interpretation (Alpert, B., Banerjee, R. and Lindqvist, L. (1974) Proc. Natl. Acad. Sci. U.S. 71, 558--562) that this was due to a tertiary structural change of the protein.

THE DEPENDENCE OF THE QUANTUM YIELD OF LIGAND PHOTODISSOCIATION FROM HAEM PROTEINS ON ULTRAFAST RECOMBINATION

Abstract— Measurements of relative photolysis yields in nanosecond flash photolysis studies of carbon monoxide and dioxygen complexes of haemoglobin and myoglobin are compared with published values of the quantum efficiency for photodissociation obtained from microsecond flash or continuous photolysis studies. It is shown that the differences in quantum yield between HbCO and MbCO and between Hb02 and Mb02 can be correlated with the different extent of ultrafast recombination observed in the nanosecond experiments. Furthermore, the temperature dependence of the quantum yield in the case of HbCO can be entirely attributed to the effect of temperature on the ultrafast recombination.

Serum Calcium, Parathyroid Hormone, and Vitamin D Status in Children and Young Adults with Sickle Cell Disease

The concentrations of serum calcium, parathyroid hormone (PTH), 25 Hydroxyvitamin D (25OHD), and 1,25 Dihydroxyvitamin D (1,25(OH)2D) were determined in 99 Saudi patients with sickle cell disease and in 104 matching healthy controls. Serum calcium and 25OHD were significantly lower in the patients, with 14% and 12% of them had serum calcium and 25OHD concentrations, respectively, below the normal range. PTH was significantly higher in the patients, with 31% having values above the normal range. There was no significant difference between patients and controls in regard to 1,25(OH)2D. There was a significant inverse correlation of 25OHD with PTH and a direct correlation of PTH with 1,25(OH)2D. Dietary intake of calcium and vitamin D was adequate in both patients and controls. The results indicate that sickle cell patients have hypocalcaemic tendency associated with supranormal PTH, and imply impaired intestinal absorption of calcium and vitamin D leading to a disturbed calcium metabolism which might contribute to the skeletal changes seen in sickle cell disease.

Photofading of basic triphenylmethane dyes: Evidence for electron transfer

Abstract The effects of a radical scavenger, 4 -hydroxy- 2 , 2 , 6 , 6 -tetramethylpiperidine-N-oxy, and an electron trap, tetracyanoethylene, on the rates of fading of two basic triphenylmethane dyes in poly(vinyl alcohol) film have been compared with their effects on the primary photochemical behaviour of the dyes on flash photolysis in a model solvent propan- 2 -ol. The presence of the electron trap markedly inhibits fading of the dyes in the film and also the observation of transient absorption on flash photolysis. The presence of other efficient electron traps, namely acetone and nitrous oxide completely inhibits transient absorption. The importance of an electron transfer step in the photofading of these dyes is discussed.

Recombination kinetics following nanosecond laser photolysis of carbonmonoxyhaemoglobin

The kinetics of the ultrafast ligand recombination following 347 nm laser photolysis of aqueous solutions of carbonmonoxyhaemogloblin have been investigated. The process is biphasic and the rate constants for the two processes as functions of temperature have been used to give activation energies of 6 +/- 3.9 kJ . mol-1 for the fast process and 31 +/- 4.8 kJ . mol-1 for the slow process. Frequency factors have also been calculated. The two processes are discussed in relation to both low-temperature studies and model calculations on the rate of entry of carbon monoxide into haem proteins.

Urinary hydroxyproline and serum alkaline phosphatase in sickle cell disease

Serum alkaline phosphatase, alkaline phosphatase isoenzymes, and urinary hydroxyproline excretion were studied in 20 young adult sickle cell patients and 58 matching normal controls. Total alkaline phosphatase was significantly higher in the sickle cell patients than in controls. Heat inactivation test and isoenzyme electrophoresis indicated that bone is the predominant isoenzyme in patients. Hydroxyproline excretion was significantly higher in the sickle cell patients than in controls. Serum total alkaline phosphatase correlated well with urinary hydroxyproline excretion in sickle cell patients (r = 0.73). Both alkaline phosphatase and hydroxyproline increased with age in the sickle cell patients. This study suggests that delayed growth and/or bone destruction may contribute to the elevated levels of alkaline phosphatase and urinary hydroxyproline.

Ultra-fast recombination in nanosecond laser photolysis of carbonylhaemoglobin

The transient absorption change observed in nanosecond laser photolysis of carbonylhaemoglobin which was previously attributed to a tertiary structural change is shown to arise from ultra-fast ligand recombination.

Photochemistry of methoxyanthraquinones

Die Blitzphotolyse der Chinone (II) in luftfreiem Benzol-Isopropanolgemisch fuhrt zur Bildung der Hydrochinone (I).